The issue of reducing water usage by cooling towers, by what could amount to millions of gallons per year for a single unit, is now at the forefront.
According to a 2015 report by Circle of Blue, a group of scientists and journalists, water rates nationally were up 41% since 2010.
By increasing the cycles of concentration used from three to six, cooling tower make-up water is reduced by 20% and blowdown is reduced by 50%.
Techniques used to reduce water requirements involve alkaline, which can destroy galvanized metal cooling towers.
Metal towers are replaced at an accelerated rate of every 7 to 10 years.
Using recycled water can save 35 to 55% on evaporation make-up water costs versus using fresh (potable) water.
Running even higher cycles can reduce water use by 40% without damaging the cooling tower.
Only 5% efficiency improvements will save you over $10,000 a year on a medium sized tower as well,
and putting in high-efficiency fan motors improves energy efficiency by 2-8%.
Unfortunately, the techniques used to reduce water requirements involve alkaline, high pH water treatment chemistries that rapidly destroy galvanized metal cooling towers. So to engage in water conservation, facility engineers are faced with the prospect of replacing galvanized metal cooling towers at the accelerated rate of every 5-8 years on average.
This is opening the door for more applications for engineered plastic cooling towers. Available from 10 to 5,000 cooling tons, the engineered HDPE (high-density polyethylene) plastic involved is impervious to very high (and low) pH water as well as other chemicals that are introduced. Such units can withstand the rigors of decades of service in the harshest industrial or environmental conditions.
For each facility, a certain amount of water loss is expected due to the nature of the evaporative process that puts the “cooling” in cooling towers. Drift, water in the form of fine mist lost into the atmosphere, is also considered unavoidable.
The water lost to both evaporation and drift must be replaced on an ongoing basis for the system to remain at full efficiency. Avoidable water loss, however, is another matter. Because the hard water used in cooling towers contains scale forming minerals (calcium and magnesium salts), the evaporative process leaves these solids behind in the water in high concentrations.
Left undiluted, these minerals cause scaling on equipment surfaces. Even a small amount of scale in the system decreases the efficiency of heat transfer, resulting in decreased productivity in industrial processes. In severe cases, scale can completely plug heat exchangers and piping.
To protect against this, some of the water is removed and replaced with fresh makeup water. The water drained from cooling equipment is called “blowdown” water or “bleed” water. The same terms apply to any unintentional water loss due to leaks, overflow, etc.
Either way, this amounts to water loss that can potentially be prevented or, at minimum, greatly reduced. Therefore, water conservation efforts are primarily focused on achieving so-called “zero blowdown” to greatly reduce the amount of makeup water required.
The primary method of reducing blowdown involves using chemical additives to impede scaling. These chemicals extend the solubility of the minerals so higher concentrations can exist in the water without causing scale or corrosion.
More advanced techniques include using treated “soft” water (no calcium or magnesium salts) through the cooling tower. Available from companies like ProChemTech, soft water chemistries such as its patented SofTek technology substantially reduce blowdown, going to zero blowdown if appropriate.
SofTek technology typically obtains a 33-40% water use reduction”, with,” says Timothy Keister, Chief Chemist/President of ProChemTech. ProChemTech is a water treatment company that designs and installs complete cooling tower, wastewater and water treatment systems. The company also offers several patented water treatment chemistries including HighCycle and SofTek to reduce water requirements.
SofTek, using 100% softened water, is an alkaline chemistry with cooling pH levels ranging from 8.5 to 9.5. This exceeds the 8.2 level at which aggressive “white rust,” so-named due to its white color rather than the typical reddish brown, becomes a major corrosion issue for galvanized metals. Although ProChemTech manages the issue with a unique white rust inhibitor, the corrosive nature of the water can still wreak havoc on traditional galvanized metal towers.
Due to the high pH of its water management programs, ProChemTech recommends and installs engineered plastic cooling towers for new construction and replacement projects so as to completely avoid any white rust corrosion issues.
In a recent application, ProChemTech was asked to redesign the furnace cooling system for Anchor Hocking Glassware. Cooling is critical for glass plants where furnaces are used to melt glass at 2200 degrees. Without water running through the system, the cooling jackets on the furnaces could build up steam and literally explode.
Four years ago, ProChemTech installed a Delta Cooling tower at Anchor Hocking Glassware’s Monaca, Pennsylvania plant to use with its SofTek chemistry. So, when the company’s Baltimore Air Coil (BAC) fluid cooler at its Lancaster, Ohio plant became so corroded it needed to be replaced, they specifically requested another tower from Delta Cooling.
In the new system, the plastic cooling tower discharges cold water into a cold well inside the plant. Cool water is then pumped through a stainless steel plate and frame heat exchanger before it is returned to the tower. Furnace cooling water is recirculated by a closed loop system which is cooled by the heat exchanger, retaining the closed loop design provided by the fluid cooler.
Anchor Hocking Glassware also asked ProChemTech to design extra capacity in the tower system to accommodate a second heat exchanger used to cool a water treatment and recycle system.
The galvanized metal tower was so thoroughly corroded that when it was removed by crane, the bottom half broke off and landed on the support structure.
He adds that the inherent and design advantages of the latest engineered-plastic cooling towers also allow easier installation (particularly on rooftops) because a lightweight plastic shell weighs as much as 40% less than a steel tower.
“Delta Cooling Towers are considerably lighter then steel. That means less money is required for support beams. This can cost a considerable amount of money,” says Keister.
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